Valve, creators of best-selling game franchises (such as Half-Life, Left 4 Dead, Team Fortress, and Counter-Strike) and leading technologies (such as Steam and Source), today announced the first game add-on for the year’s highest rated multiplatform game, Portal 2, is in development and targeted for this summer.

Portal 2 DLC #1 will offer new test chambers for players, leaderboards, challenge mode for single and multiplayer modes, and more.

Targeted for release this summer, Portal 2 DLC #1 will be offered free of charge for the PC, Mac, Xbox 360, and PS3.

Portal 2 was released April 19 and currently holds a Metacritic score of 95%, making it the top rated multiplatform game of 2011. Portal also captured the number 1 chart position in the UK, Germany, and the Nordic countries during its first week of availability, making it the fastest-selling Valve release since Half-Life 2.

A hilariously mind-bending adventure that challenges you to use wits over weaponry in a funhouse of diabolical science, Portal 2 features expansive single and cooperative multiplayer game modes.